The preparation of high performance polyolefin fibers by spinning solutions of ultrahigh molecular weight (UHMW) polyethylene (and in the Kavesh et al. applications polypropylene) to form gel fibers is described in the above applications Ser. Nos. 359,019 and 359,020 and in British Published Application No. 2,051,667 and German Offen No. 3004699 of Smith and Lemstra. In all of these references, a hot solution of the UHMW polyolefin in a solvent (with a non-polymeric stabilizer) is spun and quenched to form a gel fiber. In the Smith and Lemstra process, a volatile solvent (decalin) is used and the gel fiber is subsequently dried and stretched under defined conditions. In the Kavesh et al. process, the solvent is non-volatile (e.g. paraffin oil) and the gel fiber is extracted (e.g. with trichlorotrifluoroethane) before drying. Stretching occurs in one or more places throughout the process, and especially on the wet gel (prior to extraction) or on the dried gel or on both.
In European Published Application No. 0055001 of Stamicarbon (June 30, 1982), fillers are incorporated in the polyethylene solution prior to spinning. Both filler fibers (e.g. gypsum fibers), filler globules (e.g. glass globules) and filler particles (e.g. Aerosil.RTM. particles) are used. Certain other hydrocarbon polymers are included in the high molecular weight polyethylene described on page 5 of the reference, but the fillers described on pages 4 and 5 are essentially all inorganic materials or carbon, except for materials such as stearic acid coating the surface of reinforcing fillers such as calcium carbonate.
One preferred application for such high performance fibers is in composites. Especially when the matrix is a thermosetting resin such as an epoxy or unsaturated polyester molding compound, the polyolefin fiber itself is expected to exhibit poor adherence to the matrix. This adherence is improved in our U.S. Ser. No. 359,976 by coating the polyolefin fiber with an olefin polymer or copolymer such as low density polyethylene, ethylene acrylic acid copolymers and the like.
Other properties of the fiber which would desirably be improved for various applications include: resistance to fibrillation (e.g. in sutures and cordage), improved resistance to bending fatigue (e.g. in cordage and fabrics), moldability of the fiber itself (e.g. in composites, tents and sails), dyeability of the fiber (e.g. for textile applications) and antistatic properties (e.g. for textile applications).